1. Field of the Invention
The present invention relates generally to a method for fabricating a circuit board, and more particularly to a method for fabricating a printed circuit board having an embedded component.
2. The Prior Arts
Embedded passives are passive components disposed between layers of a multi-layer circuit board. The electronic components, such as capacitors or resistors are directly formed on an inner layer of the circuit board by etching or printing. Then, at least one outer layer of the circuit board is laminated onto the inner circuit board to bury the electronic component inside the multi-layer circuit board. The embedded passives are adapted to replace those discrete passives soldered to the circuit board, so as to free up space on the circuit board to pack more circuitry and active components.
Buried resistor technologies are first proposed by Ohmega Technologies, Inc., a manufacturer of OHMEGA-PLY® resistor-conductor material. The buried resistor is a thin film of a phosphorous-nickel alloy serving as a resistive element plated onto a matt side of a copper foil of an inner layer. Then, they are compressed to configure a thin core, and later processed by photo-resist processing twice and etching processing thrice, so as to configure a desired thin film resistor at a certain position. Such a thin film resistor is disposed between the layers, and thus called buried resistor.
In 1992, Zycon, a U.S. PCB manufacturer, proposed to further provide an extreme thin dielectric inner layer, e.g., 2 to 4 mils, in a high level multilayer circuit board in addition to original Vcc/GND inner layers. An integral capacitor is configured by the parallel copper layers of the circuit board, which provide a large area of the copper layer. Because the capacitor is disposed between the layers, it is named as buried capacitor (BC). The buried capacitor has advantages of avoiding noise, providing charging power, and stabilizing voltage, during operating at a basic frequency. With respect to the BC, Zycon owns several U.S. patents, i.e., U.S. Pat. No. 5,079,069, U.S. Pat. No. 5,161,086, and U.S. Pat. No. 5,155,655.
Recently, the concept of the embedded passives is applied to fabricate active components in the circuit board for increasing a packaging density. Accordingly, a recess is formed in an insulating layer, and an electronic component is embedded in the recess. However, the circuit board still has the insulating layer remained beneath the electronic component. Therefore, the overall thickness of the circuit board and density of the circuitry can be further improved.